Catalytic conversion of hydrocarbons



` Filed NOV. 29, 1943 Mejmafar f e/zera/or C G GERHOLVD ETAL CATALYTIC CONVERSION OF HYDROCARBONS eparazar Patented-Feb. 17, 1948 ori-ICE t cs'raLr'rrc CONVERSION 0F nYnnocAaBoNs .clarence acerhoia and John E. Burgess, ciucago. Ill., assignors to Universal Oil Products Company, Chicago, IIL, a corporation of Deia- Application November 29, 1943, serial No. '512.084

(ci. 19e-sz) 11 Claims.

The invention relates to an improved process for the catalytic conversion of fluid hydrocarbons accompanied by regeneration of the catalyst and to an apparatus in which the improved mode of operation may be conducted. The invention is particularly concerned with improvements in the regenerating step of the process which prevent subjection of the catalyst to the excessively high temperatures which cause rapid deterioration of its activity in service.

The features of the invention will be found advantageous as applied to all reactions conducted in the presence of subdivided solid contact materiali or catalyst which requires regeneration by the burning o1 combustible contaminants therefrom and which is susceptible to damage at excessively high temperatures. Reactions such as the catalytic cracking of hydrocarbon employing a siliceous catalyst, such as. for example, solid particles comprising a composite of silica with one or more metal oxides, such as alumina and zirconia. exemplify operations to which the features of the invention are particularly applicable. The following description of the invention will, therefore, be directed particularly to its features as applied to catalytic cracking.

The term cracking is `here used inabroad sense to include operations now generally termed reforming or retreatment wherein light hydrocarbon distillates, such as gasoline or gasoline fractions, naphtha and the like, are treated in the presence of cracking catalyst to improve their octane rating, susceptibility to lead tetraethyl and the like, as Well asoperations ln which oils boiling above the range of gasoline are converted to produce substantial yields of the latter or in which normally liquid or normally gaseous hydrocarbons are cracked to produce more valuable lighter fractions.

The invention is more specifically directed to an operation of the type which has recently come into prominence and wide commercial use, wherein the subdivided solid catalyst employed is cir- 2 dition of the catalyst bed in the regenerating zone is advantageous in several important respects. It facilitates circulation of the catalyst through the systemand effects a substantially uniform distribution of heat throughout the catalyst bed undergoing regeneration, thus obviating the development of localized zones of excessively high temperature within vthe bed.

It also facilitates control of the average temperature attainediwithin the bed without the use of extensive and well distributed heat exchange surfaces, such as a multiplicity of tubular elements through which cooling fluid is circulated in indirect contact with the catalyst ofthe bed to abstract excess heat therefrom.

With the use of a relatively dense uidized catalyst bed in the regenerating zone, the separation of a major portion of the catalyst particles from the outgoing stream of hot gaseous products of regeneration is effected by keeping the upper extremity of the bed well below the point in the upper portion of the regenerating vessel from which the outgoing regenerating gas is removed. This gives a light phase region above the fluid bed which has a materially reduced solid particle concentration as compared with that prevailing within the bed. A phenomenon known as afterburning sometimes occurs in this light phase rev lgion where the concentration of solid particles is they have attained a temperature at which their brought about by its contact with a hot surface in the upper portion of the regenerating vessel and once after-burning is started it is difficult to extinguish or control. In some instances it has carried over into the cyclone separating equipment communicating with the light phase and resulted in damage to the latter. which is not conveniently built to withstand high temperatures. However, greater signilcance is attached to the damage caused by after-burning to the catalyst. Cracking catalyst ol the type above mentioned, even when substantially tree of low melting components, such as alkali metal compounds. rapidly deteriorates in activity when subjected to temperatures above approximately 1300 F., or thereabouts. This is true of other catalysts commonly employed for promoting the conversion of hydrocarbons and other fluid reactants and, in some instances, extensive damage to its activity is encountered at considerably lower temperatures. Therefore. when after-burning occurs, there is a rapid decline in the activity of the catalyst. Even though the concentration of catalyst particles in the light phase is relatively, low, a major portion of the entire catalyst inventory within the system will have been present in the light phase at some time during a relatively short period of operation. Since the process is operated continuously over a prolonged period with only a small amount of catalyst replenishment to compensate for the loss of catalyst nes and keep the catalyst inventory substantially constant, even infrequent after burning will cause a pronounced decline in the average activity of the entire catalyst inventory.

The primary purpose oi' the present invention is to prevent occurrence of the aforementioned phenomenon of after-burning and resulting rapid decline in catalyst activity and possible damage to plant equipment. We have found that this can be accomplished by keeping the concentration of free oxygen suiciently low to prevent the accumulation of a flammable gas mixture in the light phase and we propose to do this by so limiting the oxygen supplied to the regenerating step that it is substantially entirely consumed during passage of the regenerating gas through the relatively dense huid-like catalyst bed. In most instances this can be done .while employing undiluted air as the oxidizing gas stream supplied to the regenerator without reducing the gas velocity in the regenerating step to such a degree that the catalyst bed is not properly uidized. It is, of course, possible to initiated. we propose to mix a controlled relatively small amount of combustible material, such as, for example, alcohol, hydrogen, hydrocarbons or the like with a sample of the outgoing regenerating gas stream and pass it through a confined zone in which it is caused to burn when there is suflicient oxygen present in the mixture to support combustion. The percentage of oxygen present in the mixture to which the extraneous fuel has been added is proportional to the temperature rise in the mixture caused by its combustion so that by measuring this increase in temperature, the percentage of oxygen in the mixture can be determined.

We have found that, under the conditions commonly employed in catalytic cracking operations of the fluid bed type, after-burning will not occur in the light phase of the regenerator when the oxygen concentration in the gas mixture is one and one-half to two percent or less by weight. By increasing the temperature in the confined zone to which the sample stream from the light phase is supplied and/or by employing a combustion promoting catalyst and insuring the presence of combustibles by adding fuel tothe sample stream, the latter will burn when the oxygen concentration is considerably less than that which would support combustion in the light phase of the regenerator. Therefore, with an oxygen analyzer of this type, measurement of the temperature rise caused by combustion in the confined zone to which the sample have a catalyst bed o such large horizontal cross-section in relation to its depth that the desired fluidization of the bed calls for an excessively large ratio of regenerating gas to catalyst volume and does not permit sufficient reduction in the rate at which regenerating gas is supplied to the bed to prevent after-burning when -air alone is employed as the incoming regenerating gas stream. This diinculty can be y avoided by proper design of the regenerating vessel and, in any rare instance` where it might be encountered in an existing installation, afterburning can be prevented by keeping the air rate sufdciently low and diluting the incoming air with suitable non-oxidizing gas, such as CO2, recycled combustion gases or the like in a sufcient amount to maintain the catalyst bed in the desired iiuid-like condition.

The most convenient and preferred method of controlling the rate at which regenerating gas of .any predetermined oxygen concentration is lsupplied to the regenerating zone so as to prevent after-burning is to determine the flammability or non-flammability of the gas mixture leaving the light phase continuously or at frequent intervals during the operation of the process and adjust the regenerating gas rate accordingly. In order to preclude after-burning and correct the operating conditions to prevent stream is supplied, will positively indicate when the oxygen concentration in the light phase is approaching the danger point and permit reduction of the volume or oxygencontent of the regenerating gas stream being supplied to the regenerator so as to preclude after-burning.

Oxygen analyzers of the anticipating type above mentioned are available on the market and do not constitute a novel part of the invention per se. However, one specic form of instrument which we have found suitable employs a coll of platinum wire or the like which acts as a combustion promoting catalyst and through which an electric current is passed. The resistance of this platinum coil increases with increasing temperature caused by burning of the sample stream passed in contact therewith so that measurement of the resistance offered by it to the passage of electrical energy therethrough indicates the oxygen Aconcentration in the sample stream. v In the preferred embodiment of the invention changes in resistance through the platinum coil or lament are translated into an impulse which is transmitted to a suitable control instrument of conventional form which functions in response to a predetermined change in the oxygen concentration of the sample stream to open and close a valve in the line admitting the regenerating gas stream to the regenerator. Thus, the occurrence of after-burning in the light phase is automatically prevented,

'I'he invention is explained in more detail in conjunction with the following description of the accompanying diagrammatic drawing.

Figure 1 of the drawing is an elevational view of one specific form of apparatus in which the improved mode of operation provided by the invention may be successfully conducted.

Figure 2 of the drawing indicates, in conjunction with its description, one specific method of controlling the free oxygen. content of the relts occurrence, rather than stop it after it is generating gas stream being supplied to the regenerator-'while maintaining its volume' substantially constant, whereby after-burning in the light phase of the regenerator can be prevented while insuring a. suilicient supply of regenerating gas to properly nuidize the catalyst bed in the regeneration 4. The reactor 3 is employed as a zone in which hydrocarbons-or other fluid reactants to be converted are contacted with a bed of subdivided solidparticlesl such as-catalyst or contact material, in the lpresence of which the reactants are converted and upon which deleterious combustible deposits are formed as a result of the conversion reaction. The regenerator 4 is employed as a zone to which contaminated catalyst or contact material is supplied from the reactor and therein contacted with oxidizing gas to burn combustible deposits from the solid particles and thus eiect their regeneration. l

A relatively dense bed 5 of the subdivided soli particles is maintained in reactor 3 and another relatively dense bed 6 of the solid particles undergoing regeneration is maintained within regenerator 4. In the type of operation to which the invention is particularly directed, the bed of solid 4particles in the regenerating zone is main` tained in a fluid-like condition, while still retaining a relatively high solid particle concentration in the bed, by passing the oxidizing gas employed for regeneration and resulting combustion gases upwardly through the bed ata velocity regulated to partially counteract the force of gravity on the solid particles and bring about their hindered settling within the bed. Preferably, the bed inthe regenerator is sufciently agitated and turbulent to obtain a substantially uniform temperature throughout the bedso as to avoid the development of hot spots or zones of localized excessively high temperature within the bed.

The approximate upper extremity of the relatively dense fiuid-like bed in regenerator 4 is indicated by the broken line 'I in the drawing and a region known as the light phase, inywhich the solid particle concentration is materially reduced relative to that prevailing in the yfluid bed 6, is maintained in the upper portion of the regenerator between the upper extremity I of the bed and the point at which the gaseous products of regeneration and solid particles oi the catalyst or contact material entrained in the outgoing gas stream are supplied to the separating equipment indicated at 8. Separator 8 may be, for example, of the centrifugal or cyclone type and is provided for the purpose of removing at least a substantial portion of the entrained' solid particles from the outgoing gas stream. The separated solid particles are re- `turned from the lower portion of separator 8 through standpipe 9 to the fluid bed 6 and gases from which the solid particles have been separated are directed from the upperl portion of separator v8 through line I0 and the pressure control valve II, preferably to heat recovery equipment of any suitable form, not illustrated.

A relatively dense stream or column of solid particles is directed from a suitable point `Within the fluid bed 6 of theregenerator downwardly lthrough standpipe I2 and through the adjustable oriilce or flow control valve I3 adjacent the lower end of standpipe I 2 into transfer line I4, wherein the streamioi'hot regeneratedsolid particles meets and commingles with the incoma ing stream of fluid reactants supplied through line I5 and valve I6. A suitable diilerential pressure is' maintained across the orice or valve I3 to prevent the upward passage of fluid reactants from line I 5 through standpipe I 2 and thel gas-lift action of the iiuid reactants effects transportation of the solid particles from column I2 through line I4 into the lower portion of re-- actor 3. In case the reactants'are supplied to line I4'in liquid state, they will be substantially vaporized by contact therein with the hot regenerated solid particles supplied from the regenerator through column I2 and the resulting mixture of essentially vaporous reactants and 'suspended solid particles is directed upwardly through the substantially conical lower head of the reactor and substantially uniformly distributed over lthe horizontal cross-section of its cylindrical portion in passing through a suitable perforate plate or distributing grid I1 provided, in the case illustrated, at substantially the Junction of the cylindrical shell with the cone botl tom of the reactor.

In the specific operation here illustrated, the bed 5 of subdivided solid particles within reactor 3 is also maintained in a fluid-like condition by the passage 0f fluid reactants and -fluid conversion products upwardly through the bed at a velocity which partially counteracts the force of gravity on the solid particles and brings about their hindered settling. Also, in the case illustrated,l a light phase region of materially reduced solid particle concentration is maintained in the upper portion of the reactor above the upper extremity I8 of the fluid bed. The mixture of fluid conversion products and suspended solid particles is di- Y rected from the light phase in the reactor to suitable solid particle separating equipment, such as the centrifugal or cyclone separator indicated at I9, wherein at least a substantial portion of the entrained solid particles are separated from the outgoing stream of iiuid conversion products. The separated solid particles are returned from the lower portion of separator I9 through standpipe 20 to the fluid bed 5. Fluid conversion products are directed from the upper portion of the separator through line 2I and pressure control valve 22, preferably to further separating, fractionating and collecting equipment of any suitable conventional form, not illustrated.

A relatively dense stream or column of solid particles is directed from any suitable point in the bed 5 of the regenerator beneath its upper extremity I8 downwardly through standpipe 23 and the adjustable orifice or now control valve 24 disposed adjacent the lower end of the standpipe into transfer line 25. In line 25, solid particles from standpipe 23 meet and commingle with a stream of oxidizing gas supplied to line 25 through line 2B and valve 2l. A suiiicient pressure drop is maintained across valve 24 to prevent the upward passage of oxidizing gas from line k25 through standpipe 23 and the gas-lift action of the oxidizing gas transports the solid particles from standpipe .23 through transfer line 25 into the lower portion of regenerator 4. The mixture of oxidizing gas employed for regeneration and the suspended solid particles passes upwardly through the conical lower head of the regenerator and is distributed -substantially uniformly over the horizontal cross-section of the cylindrical por? tion of the regenerator by means of a suitable perforate plate or distributing .grid 28 provided,

l The heat thus generated is distributed substantially uniformly throughout the fluid bed 6 by virtue of its turbulent `fluid-like condition and the relatively high concentration of solid particles within the bed. When the quantity of combustibles accumulated by the solid particles in the reactor and supplied therewith to the lregenerator is so high in relation to the average residence time for the solid particles in the regenerator that the rate at which they are burned to obtain the desired degree of regeneration would cause the development of an excessively high temperature in the iluid bed 6 of the regenerator and thus cause damage or permanent impairment to the catalyst or contact material, we contemplate preventing the development of an excessive temperature in the fluid-like bed in the regenerator by recirculating cooled regenerated catalyst therethrough. This is now a common expedient in operations oi' the iluid bed type and obviates the use of a heat exchange type regenerator containing a. large and well distributed area of heat exchange surface in the formof closely spaced tubes or the like. This controlof the average temperature in the fluid bed of the regenerator may be accomplished, for example, by withdrawlng a stream of catalyst from the upper portion of the fluid bed and returning the same through a suitable sidefarm cooler or heat exchanger to the lower portion of the regenerator for recirculation through the bed. To lavoid unnecessary complexity this feature is not illustrated in the drawing, since itis not essential in'all operations contemplated by the invention and is not a novel part of the invention per se.

To materially reduce or prevent the passage of reactants and light combustible conversion products, such as occluded hydrocarbon vapors or gases, to the regenerator in the stream of solid particles supplied thereto from the reactor, suitable stripping gas, such as steam, for example, is supplied to standpipe 23 on the upstream side of valve 24 through line 41 and valve 48. Similarly, suitable stripping gas, such as steam, for example, may be supplied through line 49 and valve 50 to standpipe I2 on the upstream side of valve I3 to substantially free the column ofvsolid particles passing through the latter of occluded oxidizing gas and combustion gases and prevent discharge line I0 through line 33, valve 34 and a suitable orifice 35 to the combustion chamber 36v of the oxygen analyzing instrument which also comprises a portion 31 in which the resistance offered by a platinum coil 38 or the like to the passage of an electric current therethrough is measured and translated into an impulse varying in magnitude with the resistance of element *line 26 of Figure 1.

38. A constant relatively small amount of fuel is supplied to the combustion chamber 36 through line 3S and orice 40 to insure the presence of combustibles in the gas mixture in the combustion chamber.A Thus, before the oxygen content of the gas in the light phase reaches a value at which combustion would occur in the latter, the presence of this smaller amount of oxygen is lndicated by burning of the mixture in chamber 36 where the combustion `reaction is catalyzed. The resulting increase in temperature in chamber 36 increases the resistance in element 38 and causes the transmission of an impulse through member 21 to controller 4I. Controller 4l is of the airoperated type, in the case illustrated, and air admitted thereto at constant pressure through line 42 and valve 43 increases the pressure in the air output line 46 from this instrument when the impulse from member 31 exceeds a. predetermined value indicating that the oxygen supply to the regenerator should be reduced. Line 46 from controller 4I is connected, in the case illus- .trated in Figure l, to control valve 21 which is a direct-acting diaphragm type valve. Thusas the oxygen concentration approaches the danger point in the light phase of the regenerator, the air pressure in line 46 reduces the opening through valve 21 to admit a smaller amount of oxidizing gas through line 26 and transfer line 21 to the regenerator. The control instruments are so adjusted that the reduced amount of oxygen being supplied to the regenerator will prevent the accumulation of a sufllcient amount of free oxygen in the light phase that the gas mixture therein is flammable under the conditions prevailing in the light phase.

Of course, any other specific form of oxygen analyzer capable of indicating the' presence of small amounts of oxygen in the sample gas stream withdrawn from the generator may be employed within the scope of the invention Also, any other conventional form of control instrument may be substituted for the type indicated at 4l and, when desired, an hydraulic or electrically operated valve of any suitable well known form may be substituted for the diaphragm type air-operated valve 21. It is, of course, also within the scope of the invention to withdraw the sample stream supplied to combustion chamber 36 directly from the light phase of the regenerator instead of from the gas discharge line I 0 and,

.when required, suitable filters or the like may be provided for removing entrained solid particles from the sample gas stream before it is supplied to the oxygen analyzer.

Referring now to Figure 2, this portion of the drawing diagrammatically illustrates a. proportioning valve which may be employed in place of the valve 21 indicated in Figure 1. The main stream of oxidizing gas, which may be air, for example, is supplied to the proportioning valve il of Figure 2 through line 26 which corresponds to Another stream of diluent gas, such as CO2, ilue gas or the like, which is substantially free of oxygen or of materially lower oxygen content than the stream supplied to line 26, is admitted to valve 5| through line |52.

The position of member 53 of the valve determines the relative proportions of oxidizing gas and diluent gas supplied through valve 5| from the respective lines 26 and 52 to transfer line 25 which corresponds to line 25 of Figure 1. However, member 53 and the` openings 54 and 55 at the valve seats are so proportioned that the total quantity of regenerating gas supplied through kstantially constant.

valve I to line 25' remains substantially constant y regardless of the position of member 53. Thus, an increase in the air pressure supplied from controller 4l through line 46 to the diaphragm or valve 5l will raise member 53 to admit less oxidizing gas and more diluent gas to line 26' while keeping the total iiow` through line 25' sub- The use of a proportioning valve, such as indicated, for example, in Figure 2, will therefore permit adjustment vof the oxygen supplied to the regenerator without material change inthe velocity of the regenerating gas passing through bed 6. Thus, this velocity can be maintained 'at a suf flciently high value to insure proper iluidization of the bed in the regenerator regardless of the rate at which oxygen is suppliedto the regenerator.

In most instances undiluted air may be employed as the total gas in line 25 without 'reduc- 21 but reverse-acting, with the suction side of a compressor or blower supplying air to the transfer line 25 so that the controller 4i will function to admit recycled combustion gases from the regenerator to the air compressor to dilute the air stream when the oxygen concentration in the light phase, as determined by the oxygen analyzer, approaches the danger point. Although the method and means whereby this type oi' control is effected is not illustrated in the drawing, it is suiliciently simple to be clear to those conversant with the art from the foregoing brief description.

- Although automatic control of the rate at which oxygen is supplied to the regenerator, so as to prevent after-burning, as provided by the A invention, is highly desirable, it is entirely Within the scope of the invention to manually control .the rate at which oxidizing gas is supplied to the regenerator or the proportion of air or oxygen in the incoming regenerating gas stream. This manual adjustment may be made in response to a visual indication furnished by the oxygen analyzer of a condition inl the light phase which requires such adjustment. i We claim:

l. In a process wherein a relatively dense fluidized bed of subdivided solid contact material, containing combustibles and susceptible to damage at high temperature, is maintained in a confined zone and oxidizing gas is passed in contact with the bed under conditions regulated to burn combustibles therefrom,` the improvement which comprisesk discharging resulting gaseous products of combustion from the bed and from said zone through a region within the latter of materially reduced solid particle concentration 'relative to that prevailing within the bed, and preventing the rapid burning of combustible components of the outgoing gas mixture within said region by limiting the free oxygenv passed in contact with the bed to a quantity which is so nearly `entirely consumed by said burning within the bed, that the' gas mixture in said region of reduced solid particle concentration is non-flammable under the conditions prevailing therein.

2. In a process wherein a relatively dense bed vof subdivided solid contact material, containing combustibles and susceptible to damage at high temperature. is maintained in a .confined zone discharging resulting 4gaseous products of combustion from the bed and from said zone through a region within the latter of materially reduced solid particle concentration relative to 'that pre- ,vailing within the bed, and preventing the rapid burning of combustible components of the outgoing gas mixture within said region by controlling the rate at which free oxygen is supplied to said, zone in said oxidizing gas in response and in inverse relation to the free oxygen content oi the gas mixture in said region of reduced solid particle concentration, whereby to keep said mixture non-flammable under the conditions pievailing in said region.

3. The method of removing combustible contaminants from substantially non-combustible subdivided solids susceptible to damage at excessively high temperature, which comprises maintaining a bed of solid particles in a confined zone, passing oxidizing gas upwardly into sald'bed at a velocity regulated to partially counteract the force of gravity on the solid particles and maintain the bed in a relatively dense. duid-like state, controlling the temperature of the bed to effect the burning of combustibles therefrom by contact with said oxidizing gas and to prevent damage to the solid particles, maintaining a region of materially reduced solid particle Aconcentration above the bed within said conned zone. discharging gaseous products of combustion from said bed and zone through said region, and controlling the rate at which free oxygen is supplied to said bed in the oxidizing gas stream to insure its substantially completel consumption within the `bed and to keep the free oxygen content of the outgoing'gas mixture suiliciently low that said mixture is non-flammable under the conditions prevailing in said region of reduced solid particle concentration.

4. The method defined in' claim 3. wherein said control of the rate at which free oxygen is supplied to the bed is effected in response and in inverse relation to the free oxygen content of the outgoing gas mixture.

5. The method defined in claim 3, wherein said oxidizing gas supplied to said bed comprises a mixture of air and diluent gas, and lwherein the velocity of the gases passing through said bed is kept substantially constant by controlling the proportionai amounts of air and diluent gas in the oxidizing gas stream while maintaining the total volume of the latter substantially constant.

6. In a process wherein a bed o f subdivided solid catalyst, contaminated with combustibles and susceptible to .damage at high temperature. is maintained in a confined zone and oxidizing gas is passed ,upwardly into said bed at a velocity regulated to keep the latter in a relatively dense. fluid-like state and under conditions regulated to burn combustibles from the catalyst particles and to regenerate the same, resultinggaseous products of combustion being discharged from the upper portion of the bedand from said zone, the improvement which comprises maintaining a light phase of materially reduced catalyst particle concentration above the fluid-like bed in the upper vportion of said conned zone to obtain within said zone a major separation of catalyst particles from the outgoing combustion gasesl and limiting the free oxygen supplied to said zone in the oxidizinggas to an amount which is substantially entirely consumed in passing through the bed, leaving the free oxygen content oi the gas mixture in said light phase suiciently low that the mixture is non-flammable under the conditions prevail- .ing in said light phase.

7. A process for the continuous catalytic conversion of uid reactants accompanied by continuous regeneration oi the catalyst which cornprises, maintaining a bed of subdivided solid catalyst capable of promoting said reaction in a conned' reaction zone, passing said duid reactants in contact with the catalysts of said bed and therein etlecting the conversion reaction with a resulting deposition of combustible contaminants on the catalyst. continuously transferring contaminated catalyst from the reaction zone to a separate confined regenerating zone, maintaining a bed of the catalyst particles in the regenerating zone, supplying a stream of oxidizing gas to the regenerating zone and into contact with the bed therein to burn combustibles from the latter, maintaining the last named bed in a relatively dense uid-like state by passing the oxidizing gas and resulting combustion gases up.- wardly therethrough at a velocity regulated to partially counteract the force of gravity on the catalyst particlesin the bed, maintaining a light phase of materially reduced catalyst particle concentration in the upper portion of the regenerating zone above said fluid-like bed, discharging gaseous products of the regeneration from said bed and from the regenerating zone through said light phase, returning a stream of regenerated catalyst particles from a point in said duid-like bed beneath its upper extremity to said reaction zone and to the catalyst bed therein. and limiting the rate at which free oxygen is supplied to the regenerating zone in said oxidizing gas stream to keep the outgoing gas mixture nonflammable in said light phase.

8. The process of claim 7, wherein said fluid reactants comprise hydrocarbons.

tion comprises the catalytic cracking of duid hydrocarbons and wherein the solid particles comprise a cracking catalyst.

10. AJ method for the regeneration ot contaminatcdV subdivided solid contact material which comprises passing an oxygen-containing gas upwardly through a mass oi said contact material in a conilned zone at a rate regulated to form a lower dense turbulent phase and an upper light phase; burning combustible contaminants from said contact material in said dense phase and controlling the temperature of said burning to avoid damaging said contact material; discharging combustion gases from the light ,phase region of said zone; and preventing the rapid burning of combustible components, such as carbon monoxide, of said combustion'gases during the passage of the latter through said light phase by limiting the oxygen contacted with said consaid contact material in the dense phase is such that it is substantially completely consumed therein.

CLARENCE G. GERHOLD.' JOHN E. BURGESS.

REFERENCES CITED The following references are of record in the file of this patent:.

UNITED STATES PATENTS Number Name Date 1,666,273 Smith Apr. 17, 1928 2,345,487 v Liedholm Mar. 28, 1944 2,073,638 Houdry Mar. 16, 1937 2,326,705 Thiele et al Aug. 10, 1943 2,353,731 Kanhofer July 18, 1944 2,378,342 Voorhees et al June 12, 1945 2,374,151 Wolk et al. z Apr. 17, 1945 2,358,039 AThomas et al.A Sept. 12, 1944 2,414,883 Martin Jan. 28, 1947 2,382,382 Carlsmith et al. Aug. 14, 1945 

